The present invention relates to a speaker device capable of stably providing a desired directivity provided by a combination of omnidirectionality and bidirectionality, down to ultra low frequencies and capable of enlarging a listening range providing excellent stereophonic feeling by a comparatively small-sized system constitution and wherein excellence is capable of enlarging a listening range providing surround effect.
Conventionally, there is known a speaker device of a closed type or an open back type. In this case, the directional characteristic at low frequencies constitutes omnidirectionality in a closed type speaker device and bidirectionality in an open-back type speaker device. Further, at middle and high frequencies where a speaker cannot be regarded as an ideal point sound source, radiated sound wave per se of the speaker is provided with directivity. That is, according to the conventional speaker device, as the directional characteristic at a low frequency region, only the omnidirectionality or the bidirectionality can be provided.
Further, FIG. 28 shows a state in which a conventional stereophonic speaker device is arranged in a test listening room 100. The speaker device is constituted by a left channel speaker device 1L having a sound signal reproducing speaker for reproducing a left channel sound signal and a right channel speaker device 1R having a sound signal reproducing speaker for reproducing a right channel sound signal.
According to such a speaker device, basically, at a listening position on a center line M of the speaker devices 1L and 1R, for example, at point a, correct sound image localization is provided between the speaker devices 1L and 1R by which inherent sound stage of a 2-channel stereophonic system is reproduced. However, at a listening position deviated from the center line M, for example, point b, there is constituted sound image localization deviated to a direction of the speaker device 1R owing to sound attenuation in distance of sound wave or the like and then inherent sound stage as the 2-channel stereophonic system is not reproduced.
That is, in FIG. 28, when sound signal reproducing speakers of the speaker devices 1L and 1R are driven by the same signal, sound image at a listening position on the center line M of the speaker devices 1L and 1R, for example, at point a, is localized in a center front direction as shown by an arrow mark. Accordingly, when ordinary stereophonic signals are reproduced, continuous sound stage is reproduced between the speaker devices 1L and 1R (illustrated by dot-dash-line La).
In this case, in respect of sound image localization of 2-channel stereophonic sound, in view of auditory sensation, the following property is known. When there is a difference in levels of sound pressures of sound waves from the speaker devices 1L and 1R, the sound image at a listening position on the center line M of the speaker devices 1L and 1R, for example, at point a, is moved in a direction of a speaker device having a higher sound pressure level. Further, when a delay time period of 1 through 30 ms is provided to either of signals for driving sound signal reproducing speakers of the speaker devices 1L and 1R, the sound image at a listening position on the center line M of the speaker devices 1L and 1R, for example, at point a, is moved in a direction of a speaker from which sound wave arrives earlier in time. This phenomenon is referred to as precedence effect, which is well known.
In view of such a property in auditory sensation, consider sound image localization at a listening position, for example, point b, deviated from the center line M of the speaker devices 1L and 1R. At point b, distances between a sound receiving point and the speaker devices 1L and 1R differ from each other and therefore, in the case where the directivities of the speaker devices 1L and 1R are omnidirectional, there causes a difference between arrival times of sound wave from the speaker devices 1L and 1R and there causes a difference in levels of sound pressures. That is, the arrival time is earlier in the case of sound wave from the speaker device 1R and the sound pressure level is higher in the case of sound wave from the speaker device 1R.
Accordingly, sound image at a listening position, for example, at point b, deviated from the center line M of the speaker devices 1L and 1R is localized to significantly deviate in a direction of the speaker device 1R as shown by an arrow mark in FIG. 28 owing to the above-described difference in sound pressure levels in addition to the precedence effect caused by time difference. Accordingly, sound stage in the case of reproducing ordinary stereophonic signals is deviated to a side of the speaker device 1R (illustrated by two-dot-dash-line Lb).
There has been proposed a method of utilizing the directivity of a conventional speaker with regard to a method of reproducing 2-channel stereophonic sound, which intends to improve the problem of deviation of the sound stage, mentioned above, that is, to enlarge the listening position providing excellent stereophonic feeling. In FIG. 29, sound signal reproducing speakers 2L and 2R of the speaker devices 1L and 1R are attached to closed type cabinets 3L and 3R such that respective principal axes (reference axes) are directed inwardly by about 45xc2x0 in view from a central listening position, which is a method of utilizing directivities provided to speakers per se at middle and high frequencies based on the fact that diaphragms of the speakers 2L and 2R are provided with limited areas. Further, in FIG. 30, as sound signal reproducing speakers 4L and 4R of the speaker devices 1L and 1R in charge of middle and high frequencies, there are used bidirectional (directivity in 8-like shape) speakers and the speakers 4L and 4R are attached to baffle plates 6L and 6R in cabinets 5L and 5R front faces of which are opened such that respective principal axes thereof are directed inwardly by about 450xc2x0 in view from a central listening position. Further, solid lines aL and aR respectively designate the directivities of the speakers 4L and 4R.
According to the examples shown by FIG. 29 and FIG. 30, by providing directivities to the sound waves radiated from the speaker devices 1L and 1R, the sound pressure level of sound wave from the speaker device 1R is reduced and the sound pressure level of left channel sound wave from the speaker device 1L is more or less increased at a listening position, for example, at point b, deviated from the center line M (refer to FIG. 28) so that the devices are operated to correct a difference between sound pressure levels based on a difference in sound attenuation in distances from the two left and right channels, whereby a listening position providing excellent stereophonic feeling is enlarged.
However, according to the example shown by FIG. 29, when the directivity is intended to provide from lower frequencies, the speakers 2L and 2R having larger apertures need to use and the system constitution becomes large-sized. Further, according to the example shown by FIG. 30, when the low frequency limit of the reproduction band is intended to widen, the baffle plates 6L and 6R attached to the speakers 4L and 4R need to enlarge. Similar to the example shown by FIG. 29, the system constitution becomes large-sized.
Further, FIG. 31 shows a state in which conventional front surround speaker devices are arranged in the test listening room 100. The speaker device is constituted by a left channel speaker device 11L and a right channel speaker device 11R. For example, the speaker device 11L is provided with a sound signal reproducing speaker for reproducing a left sound signal as well as a surround signal reproducing speaker for reproducing a surround signal, and the speaker device 11R is provided with a sound signal reproducing speaker for reproducing a right sound signal as well as a surround signal reproducing speaker for reproducing a surround signal.
In this case, the surround signal reproducing speakers are attached to speaker boxes such that principal axes thereof are directed in front directions of the speaker boxes or outwardly in respect of the front directions by predetermined angles. FIG. 31 shows an example in which principal axes of sound signal reproducing speakers 12L and 12R of the speaker devices 11L and 11R are directed in front directions FL and FR of speaker boxes 14L and 14R. Similarly, principal axes SAL and SAR of surround signal reproducing speakers 13L and 13R are directed in the front directions FL and FR. Further, FIG. 32 shows an example in which the principal axes of the sound signal reproducing speakers 12L and 12R of the speaker devices 11L and 11R are respectively directed in the front directions FL and FR of the speaker boxes 14L and 14R. In contrast thereto, the principal axes SAL and SAR of the surround signal reproducing speakers 13L and 13R are directed outwardly in respect of the front directions FL and FR by predetermined angle xcex4.
According to the front surround speaker device shown by FIG. 31, there is a drawback in which although inherent surround effect is achieved when listening is carried out at a listening position, for example, point e, on the center line M of the speaker devices 11L and 11R, the surround effect is significantly deteriorated when listening is carried out at a listening position, for example, at point f, deviated from the center line M. Hereinafter, a description will be given of significantly deteriorating the surround effect at a listening position deviated from the center line M in this way by explaining the principle of a 2-channel front surround stereophonic reproduction system.
The front surround stereophonic reproduction system is a system of achieving the surround effect by using two front speaker devices (speaker devices for left and right channels) and is a system in which sound image is produced not only in a front direction but also a transverse direction or a rear direction so that wide-angled sound stage is created in auditory sensation of a listener to provide the auditory sensation in listening to music in a wide theater to the listener. Accordingly, the front surround system is a pseudo-stereophonic sound reproduction system utilizing auditory sensation and is differentiated from an orthodox multiple-channel-stereophonic sound reproduction system, which intends to create a stereophonic actual sound field in an auditory space.
First, a 2-channel stereophonic signal is constituted by an M signal component of a monophonic signal and an S signal component providing a direction of sound image localization. That is, an L signal (left sound signal) of a left channel is a sum of two M and S components, that is, L=M+S and an R signal (right sound signal) of a right channel is a difference between the two M and S components, that is, R=Mxe2x88x92S. Accordingly, the S signal component is nothing but a signal of a difference between the L signal and the R signal and is a signal the size and the polarity of which differ depending on a direction of sound image localization.
That is, at point e on the center line M of the speaker devices 11L and 11R of FIG. 31, when sound image is localized in a front central direction, the S signal component is null and only the M signal component is constituted. Further, when sound image is localized on the left side of the front central direction, the polarity of the S signal component becomes positive similar to that of the M signal component and when sound image is localized on the right side of the front central direction, the polarity of the S signal component becomes negative different from that of the M signal component. Accordingly, the S signal component can be expressed as S=xc2x1S0, when sound image is localized on the left side of the front central direction, L=M+(+S0)=M+S0, R=Mxe2x88x92(+S0)=Mxe2x88x92S0, that is, L greater than R and when sound image is localized on the right side of the front central direction, L=M+(xe2x88x92SO)=Mxe2x88x92S0, R=Mxe2x88x92(xe2x88x92S0)=M+S0, that is, L less than R.
Next, according to the front surround stereophonic reproduction system, there is adopted a method in which in addition to the L and R signals inherent to the 2-channel stereophonic system, a surround signal mainly composed of the S signal component is superposed on said L and R signals in conformity with the polarities of the S signal components of the L and R signals and the superposed signal is reproduced electrically or the surround signal is reproduced by using exclusive speakers thereto. Although the surround signal is basically and mainly composed of the S signal component, to achieve further real surround effect, the S signal component is subjected to a signal processing of time delay, addition of reverberation or emphasizing a specific frequency component or the like. That is, the front surround stereophonic reproduction system is basically nothing but a system in which the S signal component included in the inherent L and R signals is subjected to pertinent signal processing, is further emphasized and is reproduced. By adopting such a reproduction method, intended surround effect is achieved at a listening position, for example, at point e, on the center line M of the speaker devices 11L and 11R in FIG. 31.
In this case, a physical sound condition of the reproduced sound reproduced at a listening position, for example, at point e, on the center line M of the speaker devices 11L and 11R constitutes a condition in which respective signal sound components of M, S and surround radiated from the speaker devices 11L and 11R are provided with equal magnitudes and arrive at the same time. This condition is a condition for reproducing continuous sound stage in auditory sensation between the speaker devices 11L and 11R by the two signal sound components M and S and achieving intended surround effect by the surround signal sound components, and is extremely important. However, at a listening position, for example, at point f, deviated from the center line M of the speaker devices 11L and 11R in FIG. 31, the level difference and the time difference are caused in reproduced sounds of the speaker devices 11L and 11R and then it does not satisfy the above-described condition.
Further, when the surround signals are reproduced by the exclusive speakers 13L and 13R (refer to FIG. 32 and FIG. 33), the principal axes SAL and SAR of the speakers 13L and 13R are directed in the front direction or the outward directions in view from a listening position, for example, at point e, on the center line M of the speaker devices 11L and 11R. As such surround signal reproducing speakers 13L and 13R, there are generally used small-sized speakers having an aperture of about 8 cm. In the case of a small-sized speaker having an aperture of about 8 cm, as shown by FIG. 34, a directivity which is dependent on the aperture begins to provide from a frequency of about 1 KHz and the higher the frequency, the sharper the directivity is provided.
Accordingly, in respect of the surround signal sound at a listening position, for example, at point f, deviated from the center line M of the speaker devices 11L and 11R in FIG. 31, the surround signal sound becomes larger on the right channel side and smaller on the left channel side owing to a difference in the directivities and attenuation of sound waves in distances caused by differences in directions and distances of the speaker devices 11L and 11R. Particularly, in the case in which the principal axes of the surround signal reproducing speakers 13L and 13R are directed outwardly (refer to FIG. 33), the difference in levels caused by the directivities of the surround signal sounds from the left and right channels becomes further significant. Therefore, the surround effect at a listening position, for example, at point f, deviated from the center line M of the speaker devices 11L and 11R in FIG. 31 is significantly deteriorated as mentioned above.
In view of the above-described points, it is an object of the present invention to provide a speaker device capable of stably providing desired directivity provided by a combination of omnidirectionality and bidirectionality, down to ultra low frequencies. Further, it is another object of the present invention to provide a stereophonic speaker device capable of enlarging a listening range providing excellent stereophonic feeling by a comparatively small-sized system constitution. Further, it is still another object of the present invention to provide a front surround speaker device capable of enlarging a listening range providing excellent surround effect.
According to an aspect of the present invention, there is provided a stereophonic speaker device comprising a left channel speaker device having a first speaker for reproducing a left channel sound signal and a right speaker device having a second speaker for reproducing a right channel sound signal, characterized in that a first speaker portion constituted by the first speaker of the left channel speaker device and a second speaker portion constituted by the second speaker of the right channel speaker device are provided with directivities each provided by a combination of a bidirectionality and an omnidirectionality having a maximum sensitivity on a front principal axis of the speaker and that the first speaker of the left channel speaker device and the second speaker of the right channel speaker device are attached to the speaker boxes such that principal axes thereof are inclined by a first angle respectively in a counterclockwise direction and a clockwise direction relative to front directions of the speaker boxes.
Further, according to still another aspect of the present invention, there is provided a stereophonic speaker device comprising a left channel speaker device having a first and a second speakers for reproducing a left channel sound signal and a right channel speaker device having a third and a fourth speakers for reproducing a right channel sound signal, characterized in that a first speaker portion constituted by the second speaker of the left channel speaker device and a second speaker portion constituted by the fourth speaker of the right channel speaker device are provided with directivities each provided by a combination of a bidirectionality and an omnidirectionality having a maximum sensitivity on a front main axis of each of the speakers, that the first speaker of the left channel speaker device and the third speaker of the right channel speaker device are attached to speaker boxes such that respective axes thereof coincide with front directions of the speaker boxes, and that the second speaker of the left channel speaker device and the fourth speaker of the right channel speaker device are attached to the speaker boxes such that principal axes thereof are inclined by a first angle respectively in a counterclockwise direction and a clockwise direction relative to the front directions of the speaker boxes.
The principal axes of the speakers constituting the first and the second speaker portions for reproducing sound signals of the left channel speaker device and the right channel speaker device, are directed inwardly in view from a listening position on the center line of the two speaker devices. Accordingly, by the directivities of the first and the second portions each provided by the combination of the bidirectionality and the omnidirectionality, a difference in sound pressure levels based on a difference in attenuation of sound in distances to the two left and right channels is corrected at a listening position deviated from the center line of the two speaker devices, thereby a listening range providing excellent stereophonic feeling is expanded.
According to further aspect of the present invention, there is provided a stereophonic speaker device comprising a left channel speaker device having a first speaker for reproducing a left channel sound signal and a second speaker for reproducing a surround signal and a right channel speaker device having a third speaker for reproducing a right channel sound signal and a fourth speaker for reproducing the surround signal, characterized in that the first speaker of the left channel speaker device and the third speaker of the right channel speaker device are attached to speaker boxes such that principal axes thereof are inclined by a first angle respectively in a counterclockwise direction and a clockwise direction relative to front directions of the speaker boxes, that the second speaker of the left channel speaker device and the fourth speaker of the right channel speaker device are attached to the speaker boxes such that principal axes thereof are inclined by the first angle or by a second angle different from the first angle respectively in the counterclockwise direction and the clockwise direction relative to the front directions of the speaker boxes and that a first speaker portion constituted by the first speaker of the left channel speaker device and a second speaker portion constituted by the third speaker of the right channel speaker device are provided with directivities each provided by a combination of a bidirectionality and an omnidirectionality having a maximum sensitivity on the front principal axis of each of the speakers.
Further, according to still further aspect of the present invention, there is provided a stereophonic speaker device comprising a left channel speaker device having a first and a second speakers for reproducing a left channel sound signal and a third speaker for reproducing a surround signal and a right speaker device having a fourth and a fifth speakers for reproducing a right channel sound signal and a sixth speaker for reproducing the surround signal, characterized in that the first speaker of the left channel speaker device and the fourth speaker of the right channel speaker device are attached to speaker boxes such that principal axes thereof coincide with respective front directions of the speaker boxes, that the second speaker of the left channel speaker device and the fifth speaker of the right channel speaker device are attached to the speaker boxes such that principal axes thereof are inclined by a first angle respectively in a counterclockwise direction and a clockwise direction relative to the front directions of the speaker boxes, that the third speaker of the left channel speaker device and the sixth speaker of the right channel speaker device are attached to the speaker boxes such that principal axes thereof are inclined by the first angle or a second angle different from the first angle respectively in the counterclockwise direction and the clockwise direction relative to the front directions of the speaker boxes and that a first speaker portion constituted by the second speaker of the right channel speaker device and a second speaker portion constituted by the fifth speaker of the right channel speaker device are provided with directivities each provided by a combination of a bidirectionality and an omnidirectionality having a maximum sensitivity on a front principal axis of each of the speakers.
The principal axes of the speakers constituting the first and the second speaker portions for reproducing sound signals of the left channel speaker device and the right channel speaker devices are directed inwardly in view from a listening position on the center line of the two speaker devices. Accordingly, by the directivities of the first and the second speaker portions each provided by the combination of the bidirectionality and the omnidirectionality, a difference in sound pressure levels based on a difference in attenuation of sound in distances to the two left and right channels is corrected at a listening position deviated from the center line of the two speaker devices, thereby the listening range providing excellent stereophonic feeling is expanded. Further, the principal axes of the third and the sixth speakers for reproducing the surround signal of the left channel and the right channel speaker devices are directed inwardly in view from a listening position on the center line of the two speaker devices. Therefore, at a listening position deviated from the center line of the two speaker devices, by the directivities of the speaker for reproducing the surround signal at middle and high frequencies, a difference in levels based on a difference in attenuation of sound in distances of the surround signal sound of the two left and right channels is corrected. Thus, an effect of enlarging a listening range in respect of the above-described reproduced sound for sound signal (LR signal) is added and the listening range providing excellent surround effect is further enlarged.